Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites

We report on the magnetic, resistive, and structural studies of perovskite La$_{1/3}$Sr$_{2/3}$CoO$_{3-\delta}$. By using the relation of synthesis temperature and oxygen partial pressure to oxygen stoichiometry obtained from thermogravimetric analysis, we have synthesized a series of samples with precisely controlled $\delta=0.00-0.49$. These samples show three structural phases at $\delta=0.00-0.15$, $\approx0.25$, $\approx0.5$, and two-phase behavior for other oxygen contents. The stoichiometric material with $\delta=0.00$ is a cubic ferromagnetic metal with the Curie temperature $T_{\rm C}=274$ K. The increase of $\delta$ to 0.15 is followed by a linear decrease of $T_{\rm C}$ to $\approx$ 160 K and a metal-insulator transition near the boundary of the cubic structure range. Further increase of $\delta$ results in formation of a tetragonal $2a_p\times 2a_p \times 4a_p$ phase for $\delta\approx 0.25$ and a brownmillerite phase for $\delta\approx0.5$. At low temperatures, these are weak ferromagnetic insulators (canted antiferromagnets) with magnetic transitions at $T_{\rm m}\approx230$ and 120 K, respectively. At higher temperatures, the $2a_p\times 2a_p \times 4a_p$ phase is $G$-type antiferromagnetic between 230 K and $\approx$360 K. Low temperature magnetic properties of this system for $\delta<1/3$ can be described in terms of a mixture of Co$^{3+}$ ions in the low-spin state and Co$^{4+}$ ions in the intermediate-spin state and a possible spin transition of Co$^{3+}$ to the intermediate-spin state above $T_{\rm C}$. For $\delta>1/3$, there appears to be a combination of Co$^{2+}$ and Co$^{3+}$ ions, both in the high-spin state with dominating antiferromagnetic interactions.Comment: RevTeX, 9 pages, 7 figures, to be published in Physical Review

Analysis and Prediction of Patient Survival After Radiotherapy For Liver Cancer Based On Volumetric Segmental Response and Clinically Relevant Factors

https://openworks.mdanderson.org/sumexp23/1121/thumbnail.jp

Pre-treatment tumour perfusion parameters and initial RECIST response do not predict long-term survival outcomes for patients with head and neck squamous cell carcinoma treated with induction chemotherapy

<p>Tumour plasma perfusion (F_p) in relation to overall survival (a), disease specific survival (b) and locoregional control (c). Nodal plasma perfusion in relation to survival (d) disease specific survival (e) and locoregional control (f).</p

On the effect of heterovalent substitutions in ruthenocuprates

We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8 (1212-type) ruthenocuprate, for which heterovalent doping has been achieved through partial substitution of Cu ions into the RuO2 planes (Ru1-xSr2GdCu2+xO8-d, 0<x<0.75, Tcmax=72 K for x=0.3-0.4) and Ce ions into the Gd sites (RuSr2Gd1-yCeyCu2O8, 0<y<0.1). The measurements of XANES, thermopower, and magnetization under external pressure reveal an underdoped character of all compounds. Muon spin rotation experiments indicate the presence of magnetic order at low temperatures (Tm=14-2 K for x=0.1-0.4). Properties of these two series lead us to the qualitative phase diagram for differently doped 1212-type ruthenocuprates. The difference in temperature of magnetic ordering found for superconducting and non-superconducting RuSr2GdCu2O8 is discussed in the context of the properties of substituted compounds. The high pressure oxygen conditions required for synthesis of Ru1-xSr2RECu2+xO8-d, have been extended to synthesis of a Ru1-xSr2Eu2-yCeyCu2+xO10-d series. The Cu->Ru doping achieved in these phases is found to decrease the temperature for magnetic ordering as well the volume fraction of the magnetic phase.Comment: Proceedings of the 3rd Polish-US Workshop on Magnetism and Superconductivity of Advanced Materials, July 14-19, 2002, Ladek Zdroj (Poland) to appear in Physica

Magnetic phase diagram of cubic perovskites SrMn_1-xFe_xO_3

We combine the results of magnetic and transport measurements with Mossbauer spectroscopy and room-temperature diffraction data to construct the magnetic phase diagram of the new family of cubic perovskite manganites SrMn_1-xFe_xO_3. We have found antiferromagnetic ordering for lightly and heavily Fe-substituted material, while intermediate substitution leads to spin-glass behavior. Near the SrMn_0.5Fe_0.5O_3 composition these two types of ordering are found to coexist and affect one another. The spin glass behavior may be caused by competing ferro- and antiferromagnetic interactions among Mn^4+ and observed Fe^3+ and Fe^5+ ions.Comment: 8 pages, 10 figures, revtex, accepted to Phys. Rev.